Re: Creating class using ASM

On 03/21/2011 01:27 AM, [email protected] wrote:
> at beginning i was planning to create easy class, something like :
> class myClass{
> public static void main(String arg[])
> {
> System.out.println(1);
> }
> }
>
> based on tutorial what i founded i wrote  code:
> ClassWriter cw = new ClassWriter(0);
> cw.visit(Opcodes.V1_6, Opcodes.ACC_PUBLIC +Opcodes.ACC_SUPER,
> 		    "myClass",	  // class name
> 		    null,
> 		    "java/lang/Object",
> 		    null);   // source file
>
> MethodVisitor mvc = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null,
> null);
> mvc.visitVarInsn    (Opcodes.ALOAD, 0);
> mvc.visitMethodInsn (Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>",
> "()V");
> 		mvc.visitInsn	    (Opcodes.RETURN);
> 		mvc.visitEnd();
> 		
> MethodVisitor mv = cw.visitMethod( Opcodes.ACC_PUBLIC+Opcodes.ACC_STATIC,
> 		    "main",		   // method name
> 		    "(Ljava/lang/String[];)V", // method descriptor
> 		    null,		     // exceptions
> 		    null);		     // method attributes
> mv.visitCode();
> mv.visitFieldInsn  (Opcodes.GETSTATIC, "java/lang/System", "out",
> "Ljava/io/PrintStream;");
> mv.visitInsn(Opcodes.ICONST_1);
> mv.visitMethodInsn (Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println",
> "(I)V");
> mv.visitInsn	   (Opcodes.RETURN);
> mv.visitEnd();
> cw.visitEnd();
> byte[] bytecode = cw.toByteArray();
>
> which is not working, but after i disasseble both classes, i got almost same
> code for both of them:
> public class myClass extends java.lang.Object{
>
> public myClass();
>    Code:
>     0:	aload_0
>     1:	invokespecial	#8; //Method java/lang/Object."<init>":()V
>     4:	return
> public static void main(java.lang.String[]);
>    Code:
>     0:	getstatic	#16; //Field java/lang/System.out:Ljava/io/PrintStream;
>     3:	iconst_1
>     4:	invokevirtual	#22; //Method java/io/PrintStream.println:(I)V
>     7:	return
> }
>
> where in my class made from source i have #1 #2 #3 instead of #8 #16 #22
>
> and error message when i'm trying run my class is:
> Arguments can't fit into locals in class file myClass
> can anyone tell me what i'm doing wrong
> regards

You forget to call mv.visitMax() before mv.visitEnd().

Rémi

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